Electronic timer circuits



Feb 5, 1952 G. D. HANcHETT, JR 2,584,871

ELECTRONIC TIMER CIRCUITS Filed June 28, 194e 2 SHEETS- 51mm 1v I'l/Y/t' l I guai; gig-5L 1559-1?" l INVENTOR faggi/htm@ ATTORN EY Feb. 5, 1952 G, D, HANCHETT, J'R 2,584,871

ELECTRONIC TIMER CIRCUITS Filed June 28, 1946 2 SHEETS--SHEET 2 f/ ,/l 2f ff El l] j I ,il T/f Tff, f/

ATTORNEY Patented Feb. 5, 1,952

ELECTRONIC TIMER CIRCUITSv George D. Hanchett, Jr., Millburn, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 28, 1946, Serial No. 679,988

6 Claims. (Cl. Z50-27) My present invention generally relates to elec#- tronic timer circuits, and more particularly to thyratron timer circuits.

A reliable electronic timer circuit should possess these following characteristics: it must have good reset accuracy; it must be stable and flexible as possible; and it should be relatively inexpensive to construct. It is, accordingly, animportant object of my present invention to provide a timer circuit which possesses many advantages over prior timer circuits, and which is characterized by the inclusion of a grid-controlled, gas-filled electron discharge tube as a relay device.

Another important object of my invention is to provide a thyratron timer circuit which, with relatively simple modifications, may function as a time delay relay or a time interval relay.

A further object of my invention is to provide an electronic'timer circuit which comprises essentially a positive and negative rectier and a thyratron relay.

Another object of my invention is tc provide a thyratron timer circuit adapted for a wide variety of uses such as timing the exposure of photographic paper during printing or enlargement, control of time current is applied towelding electrodes and tube high current emission testing.

Still other objects of my invention are to improve generally the efliciency and reliability of electronic timers, and more particularly to provide relatively inexpensive thyratron timing circuits which dispense with power transformers, and which utilize standard 60 cycle alternating current power relays in the thyratron plate circuit.

Still other features and objects of my invention will best be understood by reference to the following description, taken in connection with the drawings, in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into eiect.

In the drawings:

Fig. la shows a circuit diagram of a timer circuit embodying my invention;

Fig. 1b is a circuit diagram of a modication;

Fig. 2 is a schematic diagram of an illustrative use of the timer circuit;

Fig- 3 graphically'shows the timing condenser charging characteristics of the timer circuits of Figs. la and 1b;

Fig. 4 is a modification to provide a. time delay relay; and

Fig.'5 shows an additional modification wherein the circuit functions as a time interval relay.

Referring now to the accompanying drawings. where like reference numerals in the diierent figures denote similar circuit elements, I have shown in Fig. l an electronic timer circuit which possesses various advantages. Essentially the timer circuit comprises a positive rectier and a negative rectifier for the input current. That is, opposed rectiers provide rectied Ivoltages of opposite polarity. The source of input current is assumed to be connected to the leads I, I', and a 6I) cycle alternating current source may be employed. The source voltage may be chosen from 115 to 230 volts. The output leads 2, 2' deliver the cycle alternating current voltage to any desired utilization device which is to be energized at predetermined time intervals. In addition to a pair of opposed rectiers, the circuit includes a grid-controlled gas tube. The latter may be a thyratron of any well known and suitable type.

Referring more specifically to Fig. 1, the numeral 3 denotes a double diode tube which may be of the GHS or 6AL5 types. This tube provides a pair of diodes for the opposed rectifier circuits. Thus the diode D1 has its anode 4 connected to lead 5, which, in turn, is connected to the input current lead I. The cathode E is connected through resistors 'I and 8 to a lead 9, which is connected to the adjustable element I0 of a push switch. The contact II of the push, or closing, switch is connected to the input current lead I The junction of resistors I and 8 is indicated as having a potential of positive polarity relative to the low potential lead 9, and it will be noted that resistor 8 is shunted by bypass condenser I2. The second diode D2 has its cathode I3 connected to lead 5, While its anode I 4 is connected to lead 9 through the series connected resistors I5 and I5. The resistor I6 is shunted by bypass condenser I1, and the junction of resistors I5 and IIS is indicated as having a potential of negative polarity relative to the low potential lead 9. It will, therefore, 4be observed that the junctions I8 and I9 are at potentials of opposite polarity due to the fact that the respective rectiers D1 and D2 are oppositely poled.

The thyratron relay tube 20 may be of the 2050 or 2D21 types. The black dot within the tube envelope indicates that the tube is gas-filled. The cathode 2I of tube 20 is connected by lead E2 to the push switch arm I0. The plate 23 oi' the thyratron tube is connected through the winding 24 of the electromagnetic relay to the lead' 5. It will be noted that winding 24 vis shunted by resistor 25 connected in series with condenser 26. The control 'grid 21 of the thyratron tube 20 is connected through the series resistors 28 and 29 to the junction point I9. The shield grid 30 of the thyratron tube is connected to the cathode lead 22, which, in turn, is connected to the low potential output lead 2.

The cathode resistor' 8 is provided with a slider 3|, and the latter is connected by lead 32 to the adjustable arm 33 of a range switch. The latter functions to connect a desired one of three condensers 34, 35 or 36 from the junction point 31 between resistors 28 and 29 to lead 32. The electromagnetic relay is of the double pole-double throw type. The double pole-double throw switch is schematically represented, since those skilled in the electrical art are fully acquainted with the manner of constructing such a switch device which is adapted to be actuated in accordance with the energization of the relay winding 24. The double pole-double throw switch includes four contacts 38, 39, 40 and 4I. The contact 40 is open or free, while contact 4I is connected by lead 42 to the junction point 31. The contact 38 is connected by lead 43 to the lead 5, and the contact 39 is connected by lead 44 to the current input lead I.

The junction of the pair oi switch arms 45, 45 is connected by lead 46 to current output lead 2, and the junction of the pair of switch arms 41 and 41' is connected by lead 48 to the current output lead 2. It will, therefore, be seen that the pair of contacts 38 and 39 has associated with it the corresponding pair of switch arms 45 and 41, while the pair of contacts 49 and 4| has associated with it the respective switch arms 45 and 41. The mechanical structure of the switch is such' that the switch arms 45 and 45' are arranged in the manner of a seesaw, as is, also, the case of the switch arms 41 and 41. Of course, any suitable biasing device, such as a coil spring, may be used to maintain the switch arms 45 and 41 in electrical contact with contacts 40 and 4| respectively in the absence of current flow through the winding 24. Upon current flowing through winding 24, however, the switch arms 45 and 41 will be pulled into Contact with Contact points 38 and 39 respectively, thereby opening the corresponding switches 4D, 45' and 4|, 41'.

The electronic timer circuit works through one cycle of operation in the following manner. Momentarily closing push switch Ill, Il closes the electrical circuits through diodes Di, D2 and thyratron 20. This is readily seen by tracing the circuit from lead to lead 5, through diode D1, resistors 1 and 8, lead 9, switch I0, and input lead I'. A similar path can be traced through diode Dz, except that the current now flows from lead 9, resistors I6 and I5 and diode D2 to lead 5. In the case of tube 29 the circuit is traced as follows: lead I, lead 5, coil 24, plate 23, cathode 2|, lead 22, switch I0, II and lead Voltage is applied to the respective diodes D1 and D2 and to thyratron 29. As a result points I8 and I9 assume the noted respective positive and negative potentials due to the charging up of condensers I2 and |1. Concurrently, the .thyratron 20 draws current thereby energizing coil 24 whereby switches 45, 38 and 39, 41 are closed and switches 40, 45 and 4I, 41' are opened.

Closure of switches 38, 45 and 39, 41 effect respectively two actions. Switch 3B, 45 provides a path from lead I to output lead 2, while switch 39, 41 provides a path from lead I to output lead 2'. Thus, even though push switch I0, I I is only momentarily closed, the switch 39, 41 closes a shunt path across open switch I0, II. The completed circuit, then, may be traced as follows: input lead I, lead 5, lead 43, switch 38-45, lead 46, output lead 2, output lead 2', lead 48, switch 39-41, lead 44 to input lead I. Assuming that switch arm 33 has been adjusted to select timing condenser 34, as shown, as soon as condensers I2 and I1 are charged (this happens almost immediately upon closure of push switch I0, Il) condenser 34 starts to charge.

The charging of condenser 34 proceeds, since the leakage, or discharge, circuit is open. The discharge circuit is traced as follows: point 31, lead 42, switch 4I, 41', lead 48 to lead 22. The charging current flowing through resistor 29 applies a positive voltage to the thyratron grid 21, since the grid is connected through resistor 28 to the junction of resistor 29 and timing condenser 34. The thyratron cathode 2| is connected to the junction of the condensers I2 and |1. In other words, and assuming slider 3| is set at the positive or upper end of condenser I2, the input terminal of condenser 34 is connected to the positive terminal of a source of voltage (charged condenser I2) while the left end of resistor 29 is connected to the negative terminal of a second source of voltage (charged condenser I1).

Hence, adjustment of slider 3l on resistor 3 determines the period or interval during which grid 21 will be above its critical potential to permit firing of the thyratron. The size of the condenser 34, 35 or 36 chosen by switch arm 33, of course, dictates the period of time it will take to charge the timing condenser. The vslider 3| is, therefore, a fine time interval adjustment, while switch arm 33 is a coarse time interval selector switch. Eventually the grid voltage will go from a positive voltage to a negative voltage, and finally pass the point of critical grid voltage. At this point the thyratron becomes non-conductive thereby de-energizing relay coil 24. Switches 3B, 45 and 39, 41 open, while switch 4|, 41 closes. The circuit to output leads 2, 2 is broken, while the discharge circuit for condenser 34 is closed. The discharge of condenser 34 clears the system for the next cycle in response to closing push switch I0, II.

In Fig. 3 I have shown the timing condenser charging curves for a selected one of the condensers 34, 35 or 35. Grid voltages are plotted as ordinate against Time as abscissae. The grid voltage is that of grid 21. Curve A shows the characteristics secured when slider 3| is set at the upper end of resistor 8. The mark Max. time on the Time scale signifies the maximum interval or period of time secured before the thyratron is rendered non-conductive. The horizontal dash line B represents the critical grid potential of the thyratron. When curve A intersects curve B, the thyratron is rendered nonconductive. The remaining section of curve A is shown dashed to indicate the course of the curve if it were continued. Curve C represents the characteristic secured with slider 3| at the lower end of resistor 8. The legend Min. time" denotes the fact that a minimum interval of vtime elapses with this setting of slider3 I before thyratron 2U is rendered non-conductive. Between curves A and C a family of curves may be chosen, depending on the setting of slider 3|.

It will, then, be seen that in using the timer circuit of Fig. la, one must close the push switch I G, II momentarily. The timer will automatically cycle itself. To recycle the timer the same procedure is repeated. Condensers 34, 35 and 36 may have values of 0.1, 0.5 and 4.0 microfarads' respectively. These condensers should be of theI type such that they possess a good power factor.`

For example, condensers having oil or high quality paper dielectric insulation are suitable. Itis* desirable to shunt coil 24 with resistor-condenser path 25, 26 to prevent chattering due to the alternating component iiowing in the relay coil. Resistor 28 functions as an isolation resistor. proximately a :1 ratio in time can be obtained by changing the amount of positive voltage applied to the timing condenser. This variation is obtained by the position of the potentiometer 8, 3|, while greater changes in time may be obtained by selection of a larger or smaller timervv condenser with range switch 33.

The timer circuit shown in Fig. 1a possesses,`

several advantages. In the first place no power transformer is required. Standard 115 or 230 volts-60 cycle alternating current relays may be used in the thyratron plate circuit. It is necessary, however, that the resistance, inductance and capacity of the thyratron plate load circuit beso chosen that the peak and average currents are within tube ratings.

instead of carbon. Another advantage is that variations between tubes and variations through-V out life have little effect upon accuracy, as `the timer circuit always operates on the steep portion of the charging curve shown in Fig. 3. Still another advantage is the fact that the timer circuit is flexible, since large changes in time may be secured with the coarse range switch 33, while small or fine changes in time are obtained by the potentiometer 8, 3|. It can be operated from several cycles of a 60 cycle wave to approximately 2 to 3 minutes. Still further advantages are that both sides of the load are made and broken by the relay; that the timer is of the Fail-Safe type;

'that momentary contact of the push switch I0 is all that is needed to make a timer go through its operational cycle; and, nally, that the condensers are discharged after every operational cycle, allowing for immediate recycling.

The timer circuit can be used in many mechanical and electric devices. For example, it may be used to time the exposure of photographic paper during printing or enlarging. In that case the lamp of the enlarging or printing apparatus is arranged to he selectively connected to the output terminals 2, 2 of the timer circuit shown in Fig. la. Again, the timing circuit can be used for welding.

In Fig. `2 I have schematically represented such a utilization. In this gure the push switch i0, is schematically represented by the box I0'. and the input terminals l, are shown connected to the rectangle labeled Timen It will be understood that the rectangle 50 includes all the apparatus shown in la between the input terminals I, and the output terminals 2, 2 as well as the push switch. As shown in Fig. 2, the welder electrodes 5| and 52 are connected to the opposite terminals of the secondary winding of .output transformer 5,3. The output leads 2 and v.2' are, of course, connected to the opposite ends 'of the primary winding of transformer 53. In this form of utilization the timer circuit furnishes a reliable system for timing the welding of materials placed between the electrodes 5| and Again, accuracy of re-set. is maintained by the use of a relatively low value. 'of potentiometer, and this low value of resistance permits the potentiometer 8, 3| to be wire-woundv 52. The push switch is usually connected ln some manner such that the electrodes of the welder must be making good contact with the material to he welded before welding current is applied.

An additional use to iwhich the timer circuit may be put is in connection with testing high current tube emission where a series of high current pulses are applied to a tube for two seconds, and the drop across the tube must be below a certain limit. It is necessary to use a timer for this testing since a large current passing through the cathode coating would increase the temper- "ature due to the voltage drop through the coating. In this case, the timer circuit output leads are connected to a power supply source which in turn feeds a pulser which is responsive to a trigger circuit, and furnishes square wave pulses between the cathode and plate of a tube such as a thyratron. Many other uses are available with the timer circuit shown in Fig. la.

The following illustrative circuit constants are provided in order to enable those skilled in the art to construct the timer circuit, it being understood, however, that my invention is in no way limited to the specic circuit constants:

In Fig. 1b I have shown a modification of the timer system of Fig. la. The essential change involves the double contact-push switch which allows the timer to work its normal cycle even if the push switch is held in the closed position by the operator. The circuit is very similar to that shown in Fig. la, except that only two con densers 34 and 35 are used, condenser 36 being omitted. The timing condenser discharge line in Fig. 1b is traced as follows: point 31, lead 42', switch section 43', lead 42, switch 4|, 41, and lead 48. The switches I0, and 42 are mechanically interconnected, as indicated by the parallel vertical dash lines. When the push switch is actuated to close switch l0, the switch 42 is concurrently opened. Hence, the timing condenser discharge line through 42" is opened, and the discharge of condenser 34 or 35 cannot take place until switch 42 is closed again. It will. therefore, be seen that the timer circuit will open after an interval upon thyratron 20 becoming non-conductive (as explained in connection with Fig. la). However, recycling will not be had until the push switch is released, and pressed again to close switch I0, Release of the push switch permits the switch 42 to close thereby closing the discharge circuit, and clearing the timing condenser for a new cycle of timing. y

The circuit arrangement of Fig. l may with relatively simple modifications be employed asa time delay relay or a time interval relay. These two circuit functions are respectively shown in Figs. 4 and 5. It will be noted during the course of'the following description that the essential circuit elements of Figs. 4 and 5 respectively are quite similar to the circuit elements of Fig. 1a. In general, the time delay relay circuit of Fig. 4 is similar to the timer circuit of Fig. 1a, except for the fact that the grid 21 of thyratron tube 20 goes from a more negative potential to a more positive "lows: double diode starts to charge condenser l1, at

potentials The -timingcomes from the-factthat as the condenser 60 charges, thegratio orvoltages acrossthezresistances Eil and 62 will change. f'The' time interval timingcircuit of Fig.` 5 similarto the timer circuitcf Fig. 1a5exceptthat the time intervals are controlled by thecharging ofthev condenser 80 through the resistance 8l, and the discharging ofthe condenser Sli-is controlled through resistance 82. The relay in the anode circuitsof the thyratron tube 20 iscon-l ducting, or made so that it is oil when the thyratron is conducting.V Y l Y. 4Anse for-the time delay relay of Fig; 4 is lin testing tubes where,'after insertion of the tube in asocket, it is desirable to have a predetermined time before application' of plate voltage in order that 'the' heater may come up to temperature. The' time interval relay of Fig; 5 maybe usedto test filaments in' vacuum tubes,V where vthe vlilament has a derinitenumber of -heatings and coolings'throughout life. In-this case the timer may beffsoarranged that-the voltage'is applied to the filament for30 seconds and then held off Vfortwo minutes. Some of these tests go on as long as 100 hours.

Considering now.the specific circuit connections shown in the time. delay relay circuit of Fig. 4, it Will be noted that the potentiometer slider 8, 3i is arranged in theanode circuit of diode Di. Inctherwords, the cathode 6 in this case is connected to the lead 5, `While the anode 4 is cone nectedtothe low potential line 9 through the series resistors 1 and 8. The push switch i0 is adapted to connect the cathode 6 to the anode ilz4"ofidiode Dzyand the cathode of the latter diode is connected to lead'9 through. resistors I6 and i8 vwhich'arezin series.:Y The timing condenser 60 lhas its upper terminall connected through,re

sistor82 to the'junction point i9, while the lower terr'nina'lA isconnected through the lead 32 to the potentiometer slider3l. i 1 :The timing condenser 60 is shunted by a re- -s'istori t; and the control grid 21. of thyratron tube 28 'is'Y connected through isolation resistor 28` to 'the upper terminal of condenser 6l).` The 60 cycle outputleads 2 and-2 areconnected respectively `in the manner shown inFig. la; except that the plate `23 of the thyratron tube 20 includes in -its VVcircuit"V the electromagnetic relay coilI 24 which controls the opening and closing of switch 18. Theoutput lead 2 is connected to the switch arm 1i, while the fixed contact 12 of the switch l1li is corinected'to the upper end ofl relay coil `or ff'winding 24. The output lead 2' isconnected to the cathode `2i 'of the thyratron tube. The'relay Vwinding `24 isshunted, as shown' in Fig. 1a, 'oy

resistor 25 in series with condenser 26 to prevent chattering. Y

The time delay relay of Fig. 4 operates as fol* Switch l0 is closed. One-half of the the same time, condenser 80 Vstarts to charge. The charging current through resistor 82-isiirst 'negative at the gridV end, and then progresses in the positive direction. *When the critical grid value is reached the tube`20 goes-intoconduction.

and will remain there until'switch'4 l0 is open.

Switch l0 is usually av knife or toggle switch, and wouldseldombe a push switch. Resistor 6l is the dischai'geresistor for condenserl). l

f' The specific circuit connections ofthe time interval relay circuit shown in Fig. 5,- also, bear ja substantial resemblance to the circuit'of Fig. 1a.

AAs stated previouslyfthe time-interval-relay circuit diifers in that the time intervals are conan anode, l l

5 'the thyratronvis conducting.

trolledfy thecharging of'condenser 80. through theresistance 8 I. and the dischargingof `thecondenser through resistance! of small value. How#- ever, it will be noted that there is no push switch' employed i in this circuit arrangement. The schematicallyrepresented source of energizing voltage 90.4 hasone terminal thereof connected throughthe lead 5 A totheupper terminal ofthe relay winding 24, While the. opposite terminal of source90 is connected to the low potential line 22. The double diode tube 3 has the anode of diode Di connected incommon withthe cathode of diode D2 through .lead 9i tothecontact point 390i the double pole-.doublethrow switch. The contact 4| is connected to an output lead 2, and the lead.2',is connected to contact 39. The contact 38 is free.

Thecontact 4.0 is vconnected through resistorv -28 to the control grid 21 of the thyratron tube w20.,

The junction of resistors 28 and 8|,is connected through the timing condenser 88 to lead 29, there-V by connecting the lower terminal of condenser 88 tothe junction of resistors] and 8 and to the lower end of resistor 82. LThe switch arms 45 and 45 are conductively connected by lead 93 to the junction ofv resistors 28` and 8l, whileA the switch arms 41 and 41 areconnected through lead 94 to the line 5. In the time interval relay circuit of Fig. 5, itis an essential feature that ,on period can be made. when the thyratron tube 2,0 is conducting. or made so that it is "ofT when It will, also, Abe noted that there is an intermediateoutput lead 2" from the low potential side of the system.

The-operation ofthe time` interval relay is identical to the timer shown in-Fig.v la, withthe exception that there is no initiating, orpush, switch. Further, resistor 82 determines the discharge rate of condenser 80. The foff time is the time 4it takes .condenser .80 to discharge. rihe diodes Di and D2 are connected through one contact of the relay.A It is pointed out that con- Adensers l2 and I1 discharge very quickly to permit recycling.

WhilefI have indicated and 'describedseveral systems for carrying my .invention into effect, it 0 will be apparent `to one skilled'in the ',art that lmy invention is by`no means limited to the'particular circuit 1 organizations .shown and described, butA that many modifications may be Y marie without'departing from the scope of my invention.

What Iclaimis: Y Y ,1. In an apparatus for controllingthefconv'duction of pulsating"current'betweenfa"pair of `alternating current input terminals, 'the comlbination of first an'd"'s'ec'od `i'fe'ctiiier circuits connecting said terminals, eachfsaid circuit including a seri Vlly connected rctier and capacitor, said rectifiers being connectedin'said'circuits in opposite polarity to conduct current be- "Atween saidtermin'als yin opposite Vdirectionsto deyelopacross saidcapacitors voltages vof'op- `posite polaritywithl'respect to'o'ne of Vsaid input VtermirialsQ an `electron "discharge device 'having A 'aY cathode and a control grid," means connecting `said`anode"and said 'cathode `to` opposite ones of said inputy terminals to' provide'a path for pulsating current ow between said `terminals, a third circuit connected between'a P` point of positive' potential in said "rst' circuit and a point of negative potential in said second circuit, said third circuit including a serially connected resistor and a third capacitor, and means connecting said control grid to the junction point between said resistor and said third capacitor.

2. An apparatus as defined in claim 1 includ ing a resistor connected in parallel with said capacitor in said iirst circuit, and a slider conduction of pulsating current between a pair of ,g

alternating current input terminals, the combination of first and second rectifier circuits connecting said terminals, each said circuit including a serially connected rectifier and capacitor, said rectliiers being connected in said circuits to conduct current between said terminals in opposite directions to develop across said capacitors voltages of opposite polarity with respect to one of said input terminals, an electron discharge device having an anode, a cathode and a control grid, means connecting said anode and said cathode to opposite ones of said input terminals to provide a path for pulsating current fiow between said terminals, a third circuit connected between a point of positive potential in said first circuit and a point of negative potential in said second circuit, said third circuit including a serially connected resistorand a third capacitor, means connecting said control grid to the junction point between said resistor and said third capacitor, and means responsive to pulsating current iiow through said device for discharging said last named capacitor.

6. Apparatus as defined in claim 5 wherein said last named means comprises a relay having an operating winding connected serially with said tube in said path, said relay having a pair of contacts adapted to close in response to energization of said relay, said contacts being connected to opposite plates of said third capacitor GEORGE D. HANCHETT, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,552,321 Lea Sept. 1, 1925 1,917,418 Almquist July 11, 1933 1,938,742 Demarest Dec. 12, 1933 2,016,147 La Pierre Oct. l, 1935 2,165,048 Gulliksen July 4, 1939 2,269,151 Garman Jan. 6, 1942 2,304,207 Richardson Dec. 8, 1942 2,412,571 Few Dec. 17, 1946 

